1. Field of the Invention
This invention relates generally to the field of immunotherapy of cancer and infectious diseases, and more specifically, to a mixture of a controlled release vehicle containing an agent which potentiates the immune response to a tumor and tumor cells or specific antigens from tumors or pathogens. The invention includes a method for cancer therapy by immunization with the immunopotentiating mixture.
2. Description of Related Art
Active immunotherapy is considered to be a promising approach to the treatment and, particularly, to the inhibition of recurrences of human cancer. Specific active immunotherapy, one of the most promising approaches under investigation, involves activation of the host immune response against the tumor by immunization with tumor cells (which may be altered by mutagenesis, by treatment with a hapten, or by expression of foreign proteins) in order to activate specific effector cells of the immune system, such as cytolytic T lymphocytes. Nonspecific active immunotherapy may utilize microbial or chemical immunomodulators-to activate natural killer (NK) cells, macrophages, or lymphokine activated killing (LAK) cells. Unfortunately, much of the promise of these approaches remains unfulfilled.
One of the most critical questions in cancer immunology is why the immune system fails to eliminate tumors. In the 1970's, Hewitt articulated the notion that most tumors did not express any tumor-specific or neoantigens and, thus, could not be recognized as "foreign" by the immune system. Indeed, virtually no tumor cell surface antigens recognized by antibodies were found to be tumor specific, and furthermore, most spontaneous murine tumors were considered "poorly immunogenic" as defined by their failure to be eliminated when transferred into syngeneic hosts (Hewitt, etal., Br. J. Cancer, 33:241-259 1976). However, these same tumors could be rendered "immunogenic" by mutagenesis (Van Pel and Boon, Proc. Natl. Acad. Sci. USA, 79:4718-4722, 1982) when new antigens are expressed on the tumor cell surface.
It is possible that the immune system fails to eliminate tumors not because neoantigens are absent, but rather because the response to these neoantigens is inadequate. Therefore, a method for enhancing immunogenicity of the tumor cells so as to potentiate the host's immune response to these tumor cells would provide a key advance in immunotherapy.
Failure to respond to tumor neoantigens may be due, at least in part, to a failure of T cell help. The molecular basis for Th function is the local secretion of lymphokines, such as interleukin-2 (IL-2), that act upon CTLs whose T cell receptors have first been engaged by the appropriate antigen-MHC complex (reviewed in Moller, Immunol Rev. 51, 1980). The cytotoxic potential of NK and LAK cells is also enhanced by IL-2 (Grimm, et al, J. Molecular and Applied Genetics, 2:101-109, 1982; Phillips and Lanier, J. Exp. Med., 164:814-825, 1986; Ortaldo, et al., J. Exp. Med., 164:1193-1205,1986). Although potentiation of tumor immunity by systemic injection of interleukin 2 has been attempted, those studies were hampered by the toxicity of the systemically administered IL-2. Therefore, a method for potentiating immunity to tumors by providing accessory T cell help in the location of the tumor is a more attractive option, which has long been needed for cancer therapy.
An additional difficulty in immunotherapy results from the problems inherent in administration of a living tumor cell to a patient. In the past, tumor cells used for immunization were treated prior to immunization to reduce their proliferative potential, e.g., by irradiation or treatment with mitomycin C. Unfortunately, either one of these methods of inhibiting replication also significantly diminishes the immunogenicity of the cells. For example, it has been shown that mutagen induced variants that were irradiated with 8-10,000 Rads are no longer immunogenic (Sella, et al., Clin. Exp. Metastasis, 7:97-105, 1989). Similarly, murine tumor cells secreting IL-2 or IFN-.gamma. lose their immune potential after irradiation. In addition, attempts at using membrane preparations of tumor cells also fail to produce convincing evidence of an immune response. It would therefore be advantageous to develop a means for using viable cells to induce an immunogenic response to a tumor.
A controlled delivery system which will dependably release a biologically active substance (e.g., a pharmaceutical agent) in vivo into a biological fluid (e.g., fluids of gastrointestinal tract) or into a body tissue has remained an elusive goal. Biologically active endogenous substances such as cytokines, hormones, enzymes, and antibodies are usually less stable than conventional synthetic drugs in the physiological environment. The controlled delivery system thus provides a suitable means to administer these endogenous substances to a host.
A common approach to providing controlled release of an active substance is the encapsulation of the active substance within a polymer matrix (e.g., that made of hydrophilic polymers). While some combinations of a drug and particular polymers provide a suitable drug release profile, they require a relatively large quantities of synthetic materials to be delivered to the body. This is not desirable since such materials or their metabolites may not be biocompatible in vivo or may even have toxicity such as cytotoxicity or mutagenicity. Furthermore, encapsulation involves the use of organic solvents and/or heat, both of which can be harmful to peptide or proteinaceous drugs, not to mention the above-described endogenous substances.
Complex coacervation is a process of separation of colloidal solutions into two or more immiscible liquid phases. When oppositely charged polyelectrolytes are brought into contact in aqueous medium, a spontaneous phase separation occurs with the result of formation of coacervates. The coacervate is a phase where colloids (e.g., polymers) are concentrated. Coacervation has been employed to encapsulate water insoluble biologically active substances. For example, U.S. Pat. No. 4,794,000 discloses a method for preparing a pharmaceutical composition for oral administration which is based on a two phase coacervate system where erythromycin is included as the active ingredient. U.S. Pat. No. 5,051,304 discloses microcapsules formed by coacervation between gelatin and a chemically depolymerized polysaccharide wherein a variety of water immiscible substances can be included.
While these and other references generally teach the applicability of the coacervation technique to a delivery system in the form of a coacervate, the coacervate formation to encapsulate a particular substance of interest can only be achieved by carefully controlling the phase separation conditions such as the choice and concentrations of suitable polyelectrolytes, pH and temperature.
Biodegradable polymers have become a popular in vivo sustained release drug delivery system. Therefore, the biodegradable polymer concept may be modified in order to develop a technically simpler strategy to achieve paracrine cytokine production in tumor vaccines. Based on earlier studies demonstrating the superiority of local GM-CSF production in the induction of systemic antitumor immune responses (Dranoff, et al., Proc. Nat'l. Acad. Sci., USA, 90:3539, 1993), the ability of GM-CSF incorporated into cell sized gelatin-chondroitin sulfate microspheres to act as an adjuvant when mixed with irradiated tumor cells prior to immunization is possible.
Although many vehicles for sustained release of therapeutic compounds are known, no methodology has been developed which allows a host immune system to be adequately stimulated to ameliorate not only local, but also metastatic tumors, in an animal. The present invention provides techniques which answer this need.